Place the blackberries in a food processor and blend until pureed. Add in the liquid – bourbon, water, etc – anything to make the berries a bit more liquified – and blend once more. Spoon the mixture into a fine mesh sieve and press through with the back of a spoon to remove the seeds. If you like the seeds – keep them!
In a bowl, whisk together the sweetened condensed milk, vanilla extract and blackberry puree until combined.
Place the cold cream in the bowl of an electric mixer and beat on medium high speed until stiff peaks form. Fold the whipped cream into the blackberry mixture – constantly folding over and over until everything is combined. This will take a few minutes! Once everything is combined, fold in the chopped chocolate.
Pour the mixture into a parchment-lined loaf pan or a freezer container. Freeze at least 6 hours (or overnight) for best results. Serve with a few fresh mint leaves.